1. Field of the Invention:
The present invention relates to a structure of a pushbutton switch for use in a key board, etc., of electronic equipments.
2. Description of the Related Art:
Many related techniques in such a field employ in general a system including a movable contact fixedly mounted on a flexible member and a fixed contact separated away in a confronting relation from the movable contact for making and breaking a switch by making use of deformation of the flexible member caused by pressing it.
To make useable a contact of this type for those such as a full key board where importance is attached to a feeling of depressing it, the structure thereof should be adapted to have a mechanism to alter a stroke such as a coil spring between a pushbutton and a flexible member for conducting secure make-and-brake operation of the contact while increasing the stroke of depressing the pushbutton and depressing the contact with uniform depression at all times. For such a prior technique, "Word Processor File Keyboards, ESU-22 and ESU-21" available from Matsushita Electric Industrial Co., Ltd. is known for example. A keybord of this type employs as shown in its catalogue a pushbutton switch having compression coil springs of different two diameters doubly structured coaxially. This assures a stroke of the pushbutton switch by permitting a slider part provided on the lower portion of a key top to reciprocate in contact in its outside with the inside of a switch body. The lower portion of the switch body includes a switch part provided thereon. A contact of this switch part is composed of a fixed contact provided on the upper surface of a base plate and of a movable contact formed on the lower surface of the flexible member separated away from the fixed contact relation via a spacer. One end of the inside coil spring adjoins the upper portion of the movable contact in an interval, while the other end thereof is mounted on the lower portion of the key top. Moreover, both ends of the outside coil spring are respectively mounted on the lower parts of the key top and the body. Depressed here the pushbutton switch arranged as such, the larger coil spring is compressed, while the smaller coil spring is brought into contact with the flexible member. Depressed furthermore the key top, both the springs are compressed, whereby the flexible member is depressed and deformed by the smaller coil spring to permit the movable contact to make contact with the fixed contact for closing the contact.
Continued the depression furthermore, the two springs are compressed corresponding to an excess stroke, whereby the key top is brought into contact with the body and stopped.
The contact after being closed is stably depressed by the smaller coil spring, so that chattering, etc., is prevented from being produced.
However, with the arrangement described above, separate two larger and smaller coil springs are needed. Accordingly, the number of parts being needed is increased. In addition, assembly thereof, is performed while compressing the coil spring, so that the cost for the assembly is increased due to troubles such as compression buckling of the coil spring, etc.